A semiconductor manufacturing facility often uses non-descriptive containers, some of which are known as, for example, Front Opening Unified Pods (FOUPs) and Reticle Standard Mechanical InterFace Pods (RSPs) to store and transport wafers and photomasks throughout the manufacturing facility. FOUPs and RSPs provide mini environments with controlled airflow, pressure and particle counts for wafers and photomasks stored therein and thus isolate them from potential contamination. Wafers and photomasks stored in FOUPs and RSPs can be accessed by automated mechanical interfaces from production equipment, allowing them to be removed for processing or measurement without being exposed to the surrounding airflow.
FOUPs are typically used to store and transport 300 mm wafers. A FOUP has fins to hold the wafers in place and can load up to 25 wafers. Its front side is the opening door which allows robot handling mechanisms to directly access the wafers stored in the FOUP. On the other hand, RSPs are typically used for photomasks. Photomasks are also called reticles. They are typically transparent fused silica plates with a pattern defined with a chrome metal absorbing film. A photomask may also contain a pellicle to protect it from particle contamination. A pellicle is a thin transparent film stretched over a frame that is glued over one side of the photomask. A RSP has a bottom opening door which is lowered into the tool when the RSP is placed on a load port so that the photomask can be removed by the tool.
By design, the contents of FOUPs and RSPs cannot be determined by a casual visual examination. In addition, the contents of each FOUP or RSP may change multiple times during the manufacturing process. To keep track of the contents of each container, FOUPs and RSPs are often equipped with radio frequency identification (RFID) tags. A RFID tag normally has an unique identifier which is read by readers on tools and at various points in the production line. Information regarding the contents of each FOUP or RSP is stored in a relational database. The information is updated whenever the contents of a FOUP or RSP are changed. Thus, based on the unique RFID identifier associated with the RFID tag on each container and the information in the relational database, the production line can track the locations of the contents stored in each container.
FOUPs and RSPs routinely leave the manufacturing facility for additional processing or handling. Since all containers look alike and the contents of each container are not readily distinguishable, a container leaving the manufacturing facility may have unauthorized material in it. To prevent the unauthorized material from leaving the manufacturing facility, it is desired to have a system which can dynamically signal an unauthorized move of wafers and photomasks, and can destroy them if necessary.